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Boron nitride nanotubes are the next (really really tiny) big thing

Canadians are leading in the development of BNNTs, which create an ultralight, super-strong, heat-resistant material that could one day be used in everything from space shuttles to body armour.

Keun Su Kim with samples of boron nitride nanotubes, or BNNTs. The nanotubes can withstand temperatures exceeding 800 C. They also shield against dangerous radiation and can be made transparent, meaning they could be used in windshields and visors. (National Research Council of Canada)

When carbon nanotubes emerged on the scientific scene during the 1990s, it sparked bold talk of building ultralight planes, safer and more efficient cars, long-lasting super-batteries and elevators that stretch into space.

This wonder material, composed of a single cylindrical layer of carbon atoms arranged in a honeycomb pattern, proved more than 100 times stronger than steel and one-sixth the weight, not to mention 1,000 times better than copper at conducting electricity. Since their discovery, carbon nanotubes have become a multibillion-dollar market.

But a newer, some say superior, type of nanotube made out of atoms of boron and nitrogen now promises to give carbon nanotubes a run for their money, with the National Research Council of Canada at the forefront of efforts to commercially produce what could kick-start an entirely new industry.

“We hope to keep the lead,” said Benoit Simard, a principal researcher in the emerging technologies division of the NRC. “Interest is growing.”

The potential is huge. Boron nitride nanotubes, or BNNTs, are just as strong and light as their carbon cousins, but a crucial difference is their tolerance for extreme heat. Carbon nanotubes start to burn up at 400 C, while BNNTs can withstand temperatures exceeding 800 C.

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“For any application that requires flame resistance, the material is fantastic,” said Simard.

Another key difference is that BNNTs don’t conduct electricity, making them excellent insulators. They also have the ability to shield against dangerous neutron and ultraviolet radiation. But perhaps their most distinguishing feature is that they can be made into transparent materials or dyed different colours. With carbon nanotubes, you’re stuck with basic black.

Many materials offer one or a few of these characteristics, but not all, explaining why the U.S. Department of Energy’s Jefferson Lab describes BNNTs as “the most interesting stuff you may have barely heard of.”

The National Research Council became the world’s top producer of BNNTs in August 2014 with the launch of a pilot facility that can produce the material 100 to 200 times faster than previous methods. Under an electron microscope, individual nanotubes are one ten-thousandth the thickness of a human hair, but a few grams of the stuff looks like a fistful of white cotton candy or dryer lint.

Last year, the council struck an exclusive, 20-year manufacturing agreement with Tekna, based in Sherbrooke, Que., which plans to sell the material to customers in the defence, security, aerospace, biomedical and automotive sectors.

The unprecedented combination of strength, lightness and transparency of BNNTs lets the imagination run wild. Could it be possible to make a plane with transparent fuselage, something similar to Wonder Woman’s invisible, blast-proof jet?

“If you could dream that far out, I guess the answer would be yes,” said Simard, though more practical applications are in the works.

Individual nanotubes are a tiny fraction of the thickness of a human hair, but a few grams of the stuff looks a bit like cotton candy. (National Research Council of Canada)

“We have great hope in developing a new type of more resistant glass and integrating that into anything requiring transparency,” he said. “Take a windshield on an aircraft. It’s thick, heavy. You can imagine making this type of glass much thinner and therefore lighter, meaning a lighter plane overall that uses less fuel.”

The extensive network of wiring within that same plane could be also insulated with BNNT fibres, making the aircraft even lighter. For spacecraft, the reduced weight could substantially lower launch costs while shielding equipment and astronauts from radiation.

The Department of Defence is working closely with the NRC to develop transparent vehicle and body armour that’s better at withstanding blasts and can protect soldiers from fire and electrocution. Over time, as production costs fall, one could envision the material finding its way into high-end commercial vehicles, building materials and even medical equipment.

Canada has competition. Roy Whitney, president and chief executive officer of BNNT, LLC, a company based in Newport News, Va., recently began selling cotton ball samples of the material using a production method licensed from NASA and the U.S. Department of Energy. At this point, however, it seems the NRC and Tekna are still ahead in the race.

Whitney said there is great interest in using BNNTs to add strength and give unique characteristics to polymer, ceramic and metal composites while at the same time reducing their weight.

One promising area is the use of BNNTs in additive manufacturing, more popularly known as 3D printing, by which objects are printed in layers using “ink” made of laser-melted powders. Whitney said the temperatures required to liquefy the powders could be tolerated by BNNTs but would burn up carbon nanotubes. Aluminum powder, for example, has a melting point of about 600 C.

“No one has done this,” cautioned Whitney, though he said that down the road it could prove an effective way to manufacture everything from jet engine components to ultra-rugged military gear and sports equipment. Within 10 years, BNNTs will be just as common as carbon nanotubes are today in a range of products, he predicted.

Since BNNTs offer clear advantages, and were first developed not long after carbon nanotubes, why has it taken so long to produce them commercially?

The answer, Simard explained, lies in one of their most beneficial qualities: high tolerance to heat makes BNNTs challenging to work with.

The boron nitride powders used to create the material are available in industrial quantities and are relatively inexpensive. But synthesizing them into nanotubes — that is, transforming flat sheets of the molecules into stiffened cylindrical shapes — requires extreme temperatures and pressure, making the process difficult and expensive.

This has limited production capacity to just a few milligrams per batch. In 2013, for example, it’s estimated that less than 100 grams of the material was produced. But using a super-hot Tekna-supplied plasma torch to vaporize the powder in a special reactor chamber, the NRC proved it could produce kilograms of the fluff every year — and that’s just the start.

“We’ll be taking larger strides to stay ahead of the competition,” said Simard.

Keun Su Kim holds samples of boron nitride nanotubes, or BNNTs, being produced by the National Research Council at a facility in Ottawa. BNNTs offer several advantages over carbon nanotubes, which have become a multibillion-dollar market.

Tubes you can use

A few potential applications of boron nitride nanotubes:

Energy harvester

BNNTs have promising piezoelectric properties. This means the material can generate an electrical current when under mechanical stress. This quality, which carbon nanotubes do not have, creates potential for a new class of self-powered sensors, motors and energy generation devices designed to operate in harsh environments.

Transparent armour

BNNTs don’t absorb the visible part of the light spectrum, making it possible to create transparent composites for use in blast-proof, fire-resistant windshields for military vehicles as well as in visors or lightweight, hand-held shields for soldiers. The material would also protect against radiation exposure. The Department of Defence is currently working with the National Research Council on such innovations.

Fire-retardant products

Depending on their use, many types of insulation, product packaging and even clothing would be improved by being able to withstand fire and extreme temperatures. This is particularly true in the aerospace industry, where the weight of items being launched is directly correlated with rocket fuel consumption, and therefore cost. But even the construction and shipping industries could benefit as BNNT prices fall.

Cancer killer

In a 2012 study that appeared in the journal Technology in Cancer Research & Treatment, researchers from Italy’s Sant’Anna School of Advanced Studies, working with NASA’s Langley Research Center, found that adding tiny strands of BNNTs to tumours can help kill cancer cells. The nanotubes, they observed, turbo-boosted a treatment option called irreversible electroporation, which involves using short pulses of electricity to put holes in the walls of tumour cells to promote cell suicide, or apoptosis. The researchers speculated that the BNNTs helped amplify the electric fields that killed cells.

Hydrogen storage

BNNTs, like carbon nanotubes, have a tremendously high surface area. The larger the surface area, the more space there is for the nanotubes to bond with hydrogen and other molecules. Researchers speculate that this makes BNNTs an ideal candidate for efficiently storing large volumes of hydrogen — a clean-burning gas with potential to power a variety of vehicles using fuel cells.

Water desalination

Australian researchers reported in 2009 that BNNTs were highly effective at removing salt from water, compared with existing membrane-based desalination systems. Tamsyn Hilder, a computational biophysics scientist at Australian National University, found that the material is capable of rejecting 100 per cent of the salt in a solution that’s twice as salty as seawater, and it can do so when water is flowing four times faster than that in conventional desalination plants. BNNTs could lead to a “much faster and more efficient desalination process,” Hilder said.

Power generation

When lightly salted river water meets seawater, we know from Grade 10 chemistry that a process called osmosis is nature’s way of trying to balance the concentrations of each water source. To achieve balance, the water in the salt-free mixture wants to flow into the saltier mixture. When they are separated by a membrane that only water can pass through, flow between the two mixtures is measured as osmotic pressure. This pressure can be harnessed to generate clean electricity. In a 2013 paper published in the journal Nature, a team led by physicists at the Institut Lumière Matière and Institut Néel in France reported that osmotic flow through BNNTs produces electric currents with 1,000 times the efficiency of any previous system.

How BNNTs were born

Marvin Cohen, a materials scientist at the Lawrence Berkeley National Laboratory in California, is credited with first theorizing in 1994 that boron nitride nanotubes could be made. He speculated that boron and nitrogen — carbon’s periodic table cousins — formed the same strong bonds with each other that exist with carbon nanotubes. A year later his colleague Alex Zettl was first to synthesize the material in a lab.

The tubular structure at the atomic level is what gives nanotubes, whether made of carbon or boron nitride, their incredible strength. “If you apply force outside of a two-dimensional sheet, it has no strength,” said Chris Kingston, a materials scientist at Canada’s National Research Council. “But it gains stiffness when it is reinforced as a tube, and you gain these amazing mechanical properties as a result of this shape.”

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